Airport
fire safety design poses unique challenges for the fire protection
engineer. There are few other building types whose dominant focus is a
full operations cycle involving large numbers of public occupants as
well as a complex support system to enable the building function
(retail, baggage handling, security, and so on). To enable this
interaction, architecture becomes key in creating tall, open
front-of-house spaces and enabling high-frequency operations
back-of-house—all in a specific departures and arrivals cycle running in
parallel. This remains true regardless of the geographic location. This
article presents a fire safety design approach, using the fire
protection engineering process outlined in BS 7974,1 to highlight the key items that can create a practical airport terminal fire safety design.

Over
the years, the fire protection engineer has played a role in airport
design—seen as an enabler of the operational and design features.
Success relies on integration with the other design team members and
stakeholders. With operational requirements and signature architecture
forming a fundamental basis of the project, close communication with the
airport operator, their fire safety management team, as well as the
architect, from the very conceptual stages, have proven to be
fundamental to the successful design and implementation of an airport
terminal fire safety design.

The
fire protection engineer has a substantial role from concept stages,
right through to design, quantifying the agreed principles and being
part of the specification stage and onwards to construction and design
compliance on-site. For airports (like many other complex buildings and
one could suggest, in fact, any building), a robust strategy for
commissioning the fire and life safety systems and inspecting the key
elements for completeness, as well as participating in the training and
handover of a functioning fire strategy, is increasingly a required part
of the fire protection engineer's role.

Terminal
2 is located to the east of the existing Terminal 1. The building
consists of a seven-story main terminal building of approximately 70,000
m2 and a three story Pier E building of approximately 20,000 m2
in area. The state-of-the-art terminal is capable of handling up to 15
million passengers per year. At its peak, Terminal 2 was the largest
construction project in the state and employed up to 2,600 workers
on-site. Importantly, the terminal was built in a live airport
environment creating substantial logistics re-alignment on the site to
enable continuity of operations.

The
initial fire strategy concept began in 2006, culminating in completion
of the final as-built fire strategy revisions in 2012.

Irish
legislation, until recent amendments were introduced, required that
site works could not commence without prior approval of fire safety
design in the form of an approved "Fire Safety Certificate” from the
fire authority. Revised certificates were subsequently required in order
to reflect the as-built form. A change control method was adopted so
that the fire protection engineer could review changes as they arose and
subsequently address them with the fire authority. Such changes
included architectural design development and modifications arising from
on-site constructability issues.

Figure 1. QDR Process

THE FIRE PROTECTION ENGINEERING PROCESS

Airports,
due to their design, necessitate the adoption of a fire protection
engineered approach as opposed to following the recommendations of
prescriptive guidance. BS 7974 provides a basic framework for the
application of fire safety engineering and is similar in that regard to
the processes set out in other contemporary performance-based design
guides such as that developed by SFPE.2 This approach is illustrated in Figure 1.

The guidance recommends four main steps in the process:

Qualitative design review (QDR)

Quantitative analysis of design

Assessment against criteria

Reporting and presentation of results

While
all of these stages are important in developing a robust strategy, it
is during the QDR stage where the parameters that can create a
successful fire safety design are created. If the key items are not
known or identified during the QDR, the remainder of the process will
suffer. The remainder of this discussion will use the challenges met
during the design and construction of Terminal 2 as an example of items
that should be identified and addressed during the QDR stage.

THE QUALITATIVE DESIGN REVIEW (QDR)

BS 7974 identifies the main stages in the QDR process as the following:

Close collaboration during Operational
Readiness Activation Transition (ORAT) phase to understand client
needs. Provide for the safety of occupants within the building prior to
completion. Advise on legislative health & safety implications.

Agree on benchmark details. Close
liaison to agree on solutions to problems encountered during
construction.

Table 1. QDR Team Members and Responsibilities

The team formulated to carry out this process is key to the success of the final fire safety design and is discussed below.

The QDR Team
Through design and delivery of the T2
project, the interaction between the various teams and people involved
was found to be fundamental to proper design and delivery. Table 1
illustrates the relevant teams and their importance at each stage.

Review of Architectural Design, Occupant Characteristics & Fire Hazards
BS 7974 advises that the following be
considered in relation to the architectural design and occupant
characteristics of the building: building structure and layout, use(s)
and contents of the building, fire service access to the building,
occupants, ventilation systems, unusual fire hazards, planning
constraints and client requirements, including possible future options.

The Building, its Uses and Hazards
Passenger experience is key to the
architectural design aspirations behind an airport. The fire strategy
must facilitate this process. The resultant architectural design
typically consists of large and high, open spaces front-of-house for the
public, with little or no physical separation between each area to
allow a smooth transition for passengers from function to function
(check in, security, retail, departure; and the reverse function of
arrivals, immigration, baggage pickup, retail, arrivals and onwards
travel). Physical separation is required to separate back-of-house from
front-of-house.

Security and
immigration create spaces where a single direction of forward travel
must occur, and mixing of occupants at dif ferent stages in their
journey must be prevented. The most important "line” in the airport
terminal is the landside to airside line. This can be physical in parts
(particularly through back-of-house) but front-of-house this tends to be
a mix of physical barriers and staff-controlled processing lines. The
evacuation strategy must accommodate this, and prevent mixing of
processed and unprocessed passengers, as well as a major reprocessing of
passengers in the event of an evacuation.

Front-of-house
consists of large, high, open spaces, which may also be subdivided from
an evacuation perspective to control safe escape and minimize
interruption. In the absence of a physical subdivision, the role of
active smoke control systems and fire hazard and control strategies
becomes central to the fire safety design.

The
identification of fire hazards and how they are mitigated are therefore
central to the fire safety design. Terminal 2's high-volume, open plan,
front-of-house areas relied on a strategy that was based on either
suppression or the creation of maximum permitted fuel load sizes and
locations in areas where smoke from a fire could rise directly from a
fire to the ceiling above (ranging from 10-40 m in height).

The
airside environment of an airport is a highly controlled area, with all
staff and tenants operating under strict procedures and everyone
(including members of the public) being limited in terms of the items
they can transfer across the airside/ landside line. It is unusual to
have a public building where the fire load can be so well defined.

One
area of an airport terminal that requires detailed consideration is the
baggage handling area. This is where luggage is either sent to the
planes from the check-in desks or received from the planes and sent to
the baggage reclaim carousels. It generally consists of a large volume
with many baggage conveyors, sorters, platforms, walkways, open stairs
and mezzanines. Challenges encountered in this area include: treatment
of connections to steel work, appropriate means of escape signage in a
highly complex environment, maintaining compartmentation between the
handling hall and other parts of the terminal, and providing acceptable
travel distances for the trained staff occupying the space.

Unusual
fire loads need to be envisaged during the QDR also, specifically in
areas with high ceilings (i.e., >10-15 m), such as Christmas trees or
marketing promotion stands (e.g., cars on display). As always, the
flexibility of retail requirements needs to be considered, as
unrealistic fuel load controls from a fire strategy will cause
implementation problems and an unrealistic and potentially unsafe
approach as a basis for a fire strategy. That is why the retail team was
constantly involved in fire strategy decision making. For
implementation, a set of fuel load drawings were created and approved
under the process with Dublin Fire Brigade, which illustrated to the
client what type of fuel load could be located in each area and which
areas had to be sterile.

The strategy adopted for each area was:

Back-of-house areas. There was a need
for all back-of-house areas to be physically separated from the
remainder of the building for security purposes; therefore, traditional
compartmentation was adopted.

Retail areas. A cabin concept approach was
adopted based on automatic sprinkler protection and localized smoke
control designed to prevent smoke spilling to other areas.

Front-of-house areas underneath
mezzanines were provided with sprinkler protection, and smoke control
was provided underneath the floor slab to limit smoke spread to other
levels.

Front-of-house areas not directly below a floor slab in which
smoke from a fire could rise to roof level were subject to fuel load
control limits, depending on the maximum size of fire that could be
expected either due to an open retail kiosk or luggage fire.

Figure 2. Cabin Concept

The
cabin concept approach referenced above relates to a method commonly
adopted in large - volume buildings in which the fire load is located
within cabin-like structures. A retail unit within a shopping center or
airport is a prime example.

The
approach is based on the provision of a ceiling void that acts as a
smoke reservoir, as shown in Figure 2. The provision of automatic
sprinkler protection limits the fire size and volume of smoke produced.
Smoke extraction is designed to limit any spread out of the cabin. The
cabin concept is a useful approach in buildings in which, allowing smoke
to flow up to the roof, would result in significant extraction rates.
Other benefits include limiting smoke spread (and, therefore, business
disruption) to the fire unit and the maintaining of an open-unit
frontage.

Fire Service Access
In large terminal buildings, the fire
service typically wants to be able to arrive at a single control point
to receive a briefing from airport staff and assess the situation before
deciding the next steps. From there, they need to be able to access the
fire floor within a protected route and get within a reasonable
distance of the fire with an adequate supply of water. The means in
which they cross the airside/landside line is, therefore, an important
consideration.

Terminal 2 was
provided with a fire control center within which it was possible to
receive live information from the life safety systems, including the
CCTV cameras. The control center was separated from the remainder of the
terminal with 120-minute fire resisting construction and had dedicated
access direct to open air. From the fire control center, the fire
brigade could access a total of eight ventilated firefighting shafts
with dry mains provided therein. There were also two specific fire
service cross-over points within the building through which firefighters
only could pass the airside/ landside line as well as two external
routes. One external route was a passenger gate in the airside/landside
fence near the building perimeter while the other was a manned vehicle
gate that allowed access to the apron.

The
fire control center was provided with control panels for each smoke
zone and evacuation area, which allows for full control of evacuation of
the affected area. The evacuation can be phased on an automatic or
manual basis, or the decision can be taken to simultaneously evacuate
the entire terminal from the control room if considered necessary. In
addition, a microphone is provided with which direct announcements can
be given to occupants.

Dublin
Airport has an airport fire brigade who are the first-responders in any
incident. Dublin Fire Brigade are secondary responders following a
confirmed fire, and there is an agreed approach between each in terms of
overall command and the protocol to be followed in an emergency fire
situation.

The Occupants
The occupants of an airport terminal are
of a broad range of nationalities, mobility abilities, family groups,
single travelers, and a wide range of familiarity of travel. All are
focused on either departing a flight, or obtaining their luggage on
arrival and getting home. Their behavior is key to a successful
evacuation strategy.

With such focus
on their process, and at peak times in many airports such high numbers
of occupants present, the standard total evacuation policy in most
buildings can be unrealistic and even unsafe. A phased approach, where a
limited number of evacuation zones actually evacuate in a fire, is
preferred. This requires that remaining building zones be safe to
occupy.

Prescriptive codes assume
floor space factors, and resulting exit width provisions. For airports,
the occupancy is far more complex, and subject to detailed quantifying
by the airport planning team. The fire protection engineer can,
therefore, use passenger numbers that are based on the flow of people
through the terminal as dictated by the scheduled arrival and departure
of flights. The number of support staff supporting the airport services,
as well as airline staff, must also be incorporated, and these too are
subject to peak flows in a working day.

The
type of people within the building and their probable response upon
hearing an evacuation message is another factor that the design must
take into account, especially if an ASET (available safe egress time)
vs. RSET (required safe egress time) assessment is being undertaken. PD
7974-63 describes items that will have an impact on the
pre-movement time of occupants, which include security restrictions, the
possession of luggage, presence of family groups and language barriers.

Another
consideration that was taken within the T2 strategy was the possibility
of a relatively large number of mobility-impaired persons being present
within the terminal. This is due to potential religious groups
travelling to Lourdes in Europe, where one party may require assistance
at times for up to 130 persons, or sporting events for disabled
participants. Additional overflow disabled refuge areas were provided
for within the design to help cater for such a scenario and specific
staff procedures put in place.

Key
to all of the above is a competent trained fire safety team, and
credible reliance on this is key to a successful airport fire design. In
the absence of such competence, far less reliance on management must
occur.

Client Requirements & Future Flexibility
In an airport, one of the main client
requirements is that the building operates as smoothly as possible. When
dealing with a terminal building, this means that passengers are
processed without delay and security lines are maintained. This was a
fundamental challenge within the strategy, and meant that numerous lines
throughout the terminal could not be crossed, even in an emergency
situation.

An area that deserves
detailed consideration is the route the airside/landside line takes
through the building. The airside/landside line is the main security
line through which all people and objects must pass. Once on the airside
(i.e., the departure side) side of this line, a passenger or object has
been security cleared and is assumed to be fit for flight. This line
may be formed by solid walls, partial walls, doors or simply a space
occupied by staff and an x-ray machine. The position of this line needs
to be understood fully as it can affect what happens in an emergency
situation, including direction of escape, signage and zoning of fire
safety systems.

Separating the
building into different evacuation areas allowed this challenge to be
overcome, and created a solution where occupants do not pass from
airside to landside or vice versa in an emergency situation. All escape
routes are designed independently of one another. It was another key
client requirement that the building could be evacuated as an "all out”
function if required, which was also achieved within the design.

Airports
are similar to shopping centers in that they are constantly undergoing
change due to the large number of third-party organizations and tenant
areas within the building. Flexibility was built into the T2 strategy in
a number of areas. In addition to conservative figures being assumed
for the occupancy of each area, a strategy was developed that negated
the need for the provision of fire dampers within air-conditioning
ductwork, which passed between retail units.

The
strategy for the omission of dampers from the ductwork between the
retail units was based on testing undertaken for the Hong Kong
International Airport, which showed that smoke within a unit designed in
accordance with the cabin concept typically does not exceed 80°C. In
addition, the ambient air supply was maintained to provide a positive
air pressure within the ductwork, thereby reducing the likelihood of
smoke ingress and spread. It should be noted that a fire damper was
provided where the ductwork left the retail area.

Another
important stage in the project is Operational Readiness Activation
Transition (ORAT). A period within which a series of User Acceptance
Tests (UATs) are undertaken, the ORAT phase allows end-user groups to
conduct their own sets of tests and scenarios in order to build
confidence and satisfy themselves that systems are operating as
expected. On Terminal 2, this posed a unique challenge as, due to the
construction program, beneficial access had to be given to the ORAT team
while construction was being completed. It was necessary to provide
adequate levels of safety for these occupants under the Irish Safety,
Health and Welfare at Work Act. To do so, an ORAT temporary fire
strategy was put in place so that appropriate levels of safety were
maintained. The ORAT fire strategy, which evolved on a daily basis
depending on the construction work taking place that day, entailed:

Prioritization of work in certain areas to facilitate the temporary fire strategy,

Induction sessions for all RAT staff on fire safety procedures on site,

Putting in place a number of fire
marshals whose sole duties were to enforce the agreed interim fire
strategy and to lead the ORAT staff out of the building in the event of a
fire,

The provision of a temporary wireless
fire detection and alarm system while the final building systems were
being commissioned.

Way-finding
trials were also held before the building was fully completed, as part
of the ORAT process, which involved multiple events with many (4,000+)
members of the public (including mobility-impaired persons and children)
being processed through the airport as if they were departing or
arriving. Again, a specific fire strategy had to be developed and
implemented to ensure participants' welfare.

Fire Safety Objectives & Acceptance Criteria
At the start of the process, the fire
safety goals and objectives were discussed in detail with the client and
the approving authority, which allowed a set of acceptance criteria to
be established before fire strategy work commenced.

Life Safety
It was the duty of Dublin Fire
Brigade(the approving authority) to verify that adequate levels of life
safety were being met in accordance with the Irish Building Regulations.

The Second Schedule of Part B (Fire Safety) of the Building Regulations4 requires that adequate levels of life safety be achieved in new buildings by complying with five main functional requirements:

B1 – Providing adequate means of escape
measures. This goal was achieved by carrying out an ASET vs. RSET
assessment to demonstrate that untenable conditions would not occur in
the time required for occupants to escape.

B2 – Limiting the potential for fire
spread within the building over surface linings, which was achieved by
following prescriptive guidance.

B3 – Limiting the potential for fire
spread within the building by limiting compartment sizes and providing
proper compartment construction. Smoke extraction, suppression, fuel
load control and active fire safety systems were used to achieve this
goal.

B4 – Limiting the potential for external fire spread.

B5 – Providing adequate access and
facilities for the fire service. This was achieved by the provision of
dedicated and protected access routes, building suppression systems and
active ventilation.

Business Continuity
Airports operate on a continual basis and
are a critical piece of infrastructure. Therefore, large-scale
evacuations or disruption of passenger processing in a terminal is
catastrophic for the airlines and the terminal operator for commercial
and reputational reasons. Business continuity goals were, therefore,
established during the concept stage with the client.

The
strategy was the protection of sensitive areas or areas of high fire
hazard while also providing a response that was in proportion to the
event. The philosophy adopted was based on minimizing nuisance alarms by
adopting a two-stage cause and effect, which meant that only an
evacuation would be automatically instigated following a second
activation of a smoke detector. Aspirating smoke detection was also
utilized in the baggage handling hall to avoid unnecessary nuisance
alarms and implications for the baggage handling system.

If
a fire did occur, it was limited as much as possible by the control of
fuel load, either by management controlling the size of retail kiosks,
etc., or by suppression in the form of sprinklers or gaseous
suppression. Disruption was limited by evacuating only those areas
needing to be evacuated, while maintaining passenger segregation.

In
the unlikely event that a large incident did occur, it was still
feasible to initiate a full and simultaneous evacuation of the terminal.

Barbara Lane, William Ward and John Noone are with Arup.

References:

Application of Fire Safety Engineering Principles to the Design of Buildings – Code of Practice, British Standards Institution, London, 2001.